Dynamoelectric machines such as motors and generators are widely employed in industrial and commercial facilities. These machines are relied upon to operate with minimal attention and provide for long, reliable operation. Many facilities operate several hundreds or even thousands of such machines concurrently, many of which are integrated into a large interdependent process or system. Like most machinery, at least a small percentage of such motors are prone to failure. The majority of such failures can be attributed to either mechanical failures and/or thermal failures of the machine insulation.
Other than normal aging, failures are typically due to: poor or no maintenance; improper application (e.g., wrong enclosure, excessive loading, etc.); and improper installation (e.g., misalignment, bad power, inverter mismatch, etc.). Even with normal aging failures, it is desirable to provide reliable failure prediction information for such machines.
Depending on the application, the failure of a machine in service can possibly lead to system or process down time, inconvenience, and possibly even a hazardous situation. Thus, it desirable to diagnose the machinery for possible failure or faults early in order to avoid such problems. Absent special monitoring for certain motor problems, the problems may have an insidious effect in that although only a minor problem on the onset the problem could become serious if not detected. For example, insulation problems and electrical problems may not become apparent until irreversible damage has resulted. Likewise, bearing problems due to inadequate lubrication, contamination or other causes may not become apparent until irreversible damage has occurred.
Typically, to perform machine preventive maintenance, maintenance rounds are conducted where a maintenance person or vibration specialist will go to each critical machine in the plant and couple a portable recorder to each machine to measure vibrations of the machine. Vibration analysis is the established technique for determining the health of mechanical components in rotating machinery such as induction motors. The analysis of the vibration signals taken at various times is dependent on the ability to reproduce the precise location and direction of mounting of the sensor (i.e., recorder). Consequently, portable recorders are deficient in obtaining reliable vibration data as compared to accelerometers permanently installed on the motor to be monitored.
Other types of portable recorders employed for collecting data relevant to motor health are ones that collect motor flux data, motor current data and/or motor temperature data. Many such portable recorders experience problems with consistency in data recovery because of the inherent difficulty associated with placing the portable recorder in the exact same position as when the previous recording was taken.
Another method for obtaining data relating to the health of the motor is to mount current sensors (in the motor control cabinet) to the power lines feeding the motor. The current sensors collect current data which is used in current signature analysis to assess the health of the motor. However, intimate knowledge of the motor is generally required in order to conduct a thorough motor current signature analysis. But, many manufacturers of current signature analysis equipment do not have intimate knowledge of the motors that are to be analyzed with their equipment. Simply knowing the motor horsepower and line voltage is not sufficient for performing good current signature analysis. Rather, intimate details about the motor such as the number of rotor bars, rotor construction, the number of turns on the stator winding, windage and friction losses, etc. are needed. Generally, only the actual designer of the motor has such intimate information. Thus, current signature analysis devices fabricated by those other than the motor designer oftentimes result in inferior diagnostics because they are missing important motor design information. Consequently, the best such devices can do typically is provide general guidelines for spectral peaks within relatively broad frequency ranges and try to trend from sample to sample. Additionally, such current sensor devices located in the motor cabinets cannot monitor for vibration and temperature which are two important indicators of the health of the motor. In particular, mechanical problems of a motor usually are manifested most prominently via vibrations. Thus vibration analysis is still the desired method for analyzing a machine for mechanically related problems.
Furthermore, because such monitoring typically takes place at the motor, motor diagnosis related thereto may require large amounts of manpower to collect the data and then provide a remote computer with the data to perform analyses thereon. Moreover, such manual intensive methods are not amenable to performing trend analysis.
In view of the above, there is a need for an integrated dynamometric machine diagnostic device which affords for measuring vibration, current, temperature, voltage, shaft position and other parameters relating to the health of the machine. Furthermore, it would be desirable to have such a diagnostic device which also has stored therein detailed design information of the machine it is operatively coupled to. Moreover, it would be desirable to have such a diagnostic device be part of a distributed machine diagnosis system so as to allow for on-line monitoring of a plurality of machines.